This invention relates generally to mixed-metal carbonate precursors, to the mixed-metal oxides prepared from those precursors, and to mixed-metal oxide absorbents prepared from either the precursors or the oxides. The absorbents provide a high capacity, regenerable system for the removal of both CO.sub.2 and water from air. Such a dual function system provides advantages in numerous applications (e.g., enclosed environments such as space stations, extravehicular activities, under water missions) because it saves weight and space and simplifies operation (e.g., regeneration of only one rather than two units is necessary).
In the past, CO.sub.2 has been removed from a gas by using zeolites, carbon molecular sieves, and lithium hydroxide. (See Fukunage et al., I&EC Process Design Develop., 7, 269 (1968); Dell'Osso et al., I&EC Process Design Develop., 8, 469 (1969); Dell'Osso et al., I&EC Process Design Develop., 8, 477 (1969); Zinnen et a1., U.S. Pat. No. 4,810,266; and Bovard, U.S. Pat. No. 3,684,712.) However, problems with low CO.sub.2 capacity and poor regenerability have limited the use of these absorbents. Single component metal oxide absorbent systems have also been used in the past. (See Colombo et al., Chem. Engr. Progr. Sympos. Series. 62 (63), 89-94 (1966); Barnes et al., J. Chem. Soc. (A), 3395 (1971).) Other related systems include metal hydroxides, hindered amines and other amine solutions, glycine-activated K.sub.2 CO.sub.3 solution, solid amines, supported K.sub.2 CO.sub.3, and an electrochemical depolarized CO.sub.2 concentrator system. These systems and those mentioned above are basically for the removal of CO.sub.2 only; water is typically removed by a second system, either by a condensation method or with a dryer system.